Red Oak FAQ

What is red oak?
How does red oak differ from other oaks?
How sustainable is red oak?
What is red oak best used for?
Can red oak be used externally?
Can red oak be treated with preservative chemicals?
How does American red oak compare structurally with European oak, American white oak and tropical hardwood species?
How do the individual characteristic values for red oak (designated strength class D40) compare with those of European oak (designated strength class D30)?
How does American red oak compare to European oak using BS 5268-2 permissible stress design principles?
How do the permissible stress design values of American red oak, (designated strength class D40), compare to those of the tropical hardwoods listed in the same strength classification?

1. What is red oak?

Red oak is a true Quercus, in the same group of species as European oak and American white oak. It is similar in most respects, but has some differences in characteristics and properties.

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2. How does red oak differ from other oaks?

Red oak resembles white oak and European oak in appearance, but its heartwood usually has a pinkish tinge. The vast geographical area over which red oak grows gives rise to greater variation in its structure and quality than is found in white oak. The timber is generally coarser in texture than the other two major oaks with smaller rays resulting in a less prominent silver grain figure so characteristic of oaks in general. These features of red oak enable a greater variety of colour and grain variations to be sorted thus allowing more diverse options with which designers can work.

The working properties of red oak (machining, nailing, screwing and finishing) are similar to those of white oak, however, for gluing, red oak is superior.

For structural applications, red oak is superior to European oak in strength and stiffness and is stronger in bending than white oak.
Table of Design Values for use with Eurocode 5 and BS 5268-2

Due to its open pored structure, red oak is more easily penetrated with preservatives than either white oak or European oak.

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3. How sustainable is red oak?

The area of hardwood forests in the US has risen consistently over the past 50 years. Published data (2000 RPA Assessment) shows that the area of hardwood and mixed hardwood/softwood timberlands increased by 18% between 1953 and 1997.

In the period 1953 to 2002, the inventory of hardwoods standing in the US forests has doubled as harvested levels have remained well below the level of forest growth (see table below). As a consequence, the stock of red oak has similarly increased and now stands at 35% of the hardwood forests of the eastern United states, making this timber one of the most sustainable hardwoods in the world.

Table:- Change in US hardwood inventory 1953 – 2002 (millions m³)

Millions m³	1953	2002
Inventory	5,213	10,316
Growth	176	283
Harvested Volume	116	167
Excess growth over harvest	25	40
Source:- 2000 RPA Assessment from US Forest Service

Red oak is not native to other parts of the world but is unique to North America and is not commercially available from any other source.

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4. What is red oak best used for?

Construction (both structural and non-load bearing), furniture, flooring, architectural interiors, internal joinery and mouldings, doors, kitchen cabinets, panelling, coffins and caskets.

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5. Can red oak be used externally?

The natural durability classification of red oak, as listed in EN 350-2, is class 4 – slightly durable for heartwood and class 5 – not durable for the sapwood. Based on this classification red oak is deemed to possess insufficient natural durability for external applications. However, in practice it can be used externally if the correct design, detailing and construction techniques have been adopted, along with an effective preservative pre-treatment.

Red Oak	EN 350-2
Heartwood	Class 4 - Slightly durable
Sapwood	Class 5 - Not durable

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6. Can red oak be treated with preservative chemicals?

Red oak can be treated and takes preservative chemicals more easily than does white oak.

Red Oak	EN 350-2
Heartwood	Treatability Class 2-3 (Moderately easy to treat/ difficult to treat)
Sapwood	Treatability Class 1 (Easy to treat)

Red oak absorbs more treatment application than other oaks.

[Treatability cannot be exactly defined, therefore, the treatability classes cannot be separated exactly from each other. This applies particularly to the treatabilty classes 2 and 3 (red oak heartwood). Wood species assigned to these treatability classes often show very irregular penetration.]

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7. How does American red oak compare structurally with European oak, American white oak and tropical hardwood species?

Points to note:

Red Oak is 33% stronger than European oak in bending.
Red Oak has the same strength classification as the African iroko, Australian jarrah and Asian teak.

	Hardwood Strength Classes
	Weakest---------------------------------------------------------------Strongest
	D30	D35	D40	D50	D60	D70
Bending Strength N/mm²	30 Temperate - European Oak ¹ - -	35	40 Temperate - Jarrah ² AMERICAN RED OAK Tropical - Iroko Teak - -	50 Temperate - Karri ² American White Oak Tropical - Keruing Opepe Merbau	60 Tropical - Ekki Kapur Kempas	70 Tropical - Balau Greenheart
Notes:- European oak is designated Strength Class D30 in BS 5268-2 To be visually strength graded HS (tropical timber) according to Table 14 of BS 5268-2

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8. How do the individual characteristic values for red oak (designated strength class D40) compare with those of European oak (designated strength class D30)?

Points to Note

Red oak is stronger than European oak for all characteristics except tension perpendicular to the grain where it has parity.
Tensile strength perpendicular to the grain is a measure of the resistance of wood to forces acting across the grain that cause splitting.

Characteristic Values	European Oak Strength Class D30¹	American Red Oak Strength Class D40²	% Comparison of Red Oak to European Oak
Bending – parallel to grain	30 N/mm²	40 N/mm²	+33%
Tension – Parallel to grain	18 N/mm²	24 N/mm²	+33%
Tension – perpendicular to grain	0.6 N/mm²	0.6 N/mm²	Same
Compression – parallel to grain	23 N/mm²	26 N/mm²	+13%
Compression – perpendicular to grain	8 N/mm²	8.8 N/mm²	+10%
Shear – parallel to grain	3 N/mm²	3.8 N/mm²	+26%
Mean MOE – parallel to grain	10000 N/mm²	11000 N/mm²	+10%
5% MOE – parallel to grain	8000 N/mm²	9400 N/mm²	+17%
Mean MOE – perpendicular to grain	640 N/mm²	750 N/mm²	+17%
Mean shear modulus	600 N/mm²	700 N/mm²	+16%
Characteristic density	530 kg/m³	590 kg/m³	+11%
Average density	640 kg/m³	700 kg/m³	+9%
Notes:- As designated in BS 5268-2 As allocated by BRE

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9. How does American red oak compare to European oak using BS 5268-2 permissible stress design principles?

Points to Note

Red oak is stronger than European oak for all values except stiffness where it has a slightly lower value i.e. for virtually the same stiffness factor, red oak is 83% stronger in bending than European oak.
The “stiffness” (MOE) property is important when determining the deflection of a beam under load – the greater the stiffness, the less the deflection. Stiffness is usually considered in conjunction with bending strength, as for many uses, stiffness is the controlling factor in design.

Permissible Stresses and Moduli of Elasticity (BS 5268-2)	Actual Values		% increase Am. Red Oak over Eur. Oak
	European Oak¹	American Red Oak²	% increase Am. Red Oak over Eur. Oak
Bending – parallel to grain ¹	9.6 N/mm²	17.6 N/mm²	+83%
Tension – parallel to grain ¹	5.8 N/mm²	10.5 N/mm²	+81%
Compression – parallel to grain	9.3 N/mm²	12.2 N/mm²	+31%
Compression – perpendicular to grain	3.0 N/mm²	4.6 N/mm²	+53%
Shear – parallel to grain	2.0 N/mm²	2.3 N/mm²	+15%
Mean MOE – parallel to grain	12,500 N/mm²	12,200 N/mm²	-2%
Min. MOE – parallel to grain	8,500 N/mm²	8,400 N/mm²	-1%
Characteristic density	569 kg/m³	633 kg/m³	+11%
Mean density	680 kg/m³	700 kg/m³	+3%
Notes:- Values applicable for timber up to 100 mm thick Values as per BS 5268-2 Values determined by BRE using the same methodology as in BS 5268-2

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10. How do the permissible stress design values of American red oak, (designated strength class D40), compare to those of the tropical hardwoods listed in the same strength classification?

Points to Note

Red oak is stronger in bending parallel to the grain, tension parallel to the grain, compression perpendicular to the grain and shear parallel to the grain.
The stiffness or red oak is greater than that of teak and has a slightly lower value when compared to African iroko and Australian jarrah and Asian teak.

Permissible Stresses & Moduli of Elasticity (BS 5268-2)	American Red Oak¹	Hardwood Species²
Permissible Stresses & Moduli of Elasticity (BS 5268-2)	American Red Oak¹	African Iroko	Australian Jarrah	Asian Teak
Bending – parallel to grain (N/mm²)	17.6	12.6	13.8	13.7
Tension – parallel to grain (N/mm²)	10.5	7.5	8.2	8.2
Compression – parallel to grain (N/mm²)	12.2	12.6	14.2	13.4
Compression – perpendicular to grain (N/mm²)	4.6	2.8	3.1	3.1
Shear – parallel to grain (N/mm²)	2.3	1.6	2.0	1.7
Mean MOE – parallel to grain (N/mm²)	12200	12500	12400	10700
Min MOE – parallel to grain (N/mm²)	8400	8500	8700	7400
Characteristic density (kg/m³)	633	-	-	-
Mean density (kg/m³)	700	-	-	-
Note:- TH1 grade to BS 5756 HS grade to BS 5756

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